Methods and devices for continuous production of polymeric dispersions

ABSTRACT

The present invention is directed to the use of continuous extrusion devices to form high quality polymer dispersions of polyvinyl butyral), a surfactant, and a plasticizer. Screw extruder devices of the present invention inject water into a zone of high pressure, temperature, and shear to cause the rapid inversion of a weld in less than, for example, one minute, which compares very favorably with conventional batch methods, which can take, for example, two or more hours to complete an inversion. This rapid inversion—a surprising result given the extended time inversion requires in batch processes—allows for the continuous production of poly(vinyl butyral) dispersions.

CROSS-REFERENCE TO RELATED APPLICATION

This present application is a continuation from U.S. Non-Provisionalapplication Ser. No. 14/013,316 filed Aug. 29, 2013 which is acontinuation from U.S. Non-Provisional application Ser. No. 11/274,534filed Nov. 15, 2005, now abandoned, the disclosures of which areincorporated herein by reference in their entirety

FIELD OF THE INVENTION

The present invention is in the field of polymer dispersions, and, inparticular, the present invention is in the field of polymer dispersionsthat can be applied to the surfaces of items to provide a physicalbarrier. In particular, dispersions produced by the methods of thepresent invention can be used in the formation of films or forimpregnating and coating fibrous materials, and can also be mixed withinorganic additives such as calcium carbonate or metal oxides forforming barrier coatings that can be used for paper and paperboardproducts.

BACKGROUND

Polymer dispersions, which can be polymer emulsions or polymersuspensions without a plasticizer, have conventionally been used for awide array of applications, including, for example, as a protective,temporary film coating, as paint masking, as spray booth coating, forequipment protection, and for surface decontamination.

One conventional method for producing an emulsion of plasticizedpolymer-in-water involves mixing polymer, plasticizer, and surfactant toform a weld. The weld is then mixed while sufficient water is added tocause an inversion to a plasticized polymer-in-water emulsion orabbreviated oil-in-water emulsion (see, for example, U.S. Pat. No.2,487,254). The oil-in-water emulsion can then, for example, be sprayedon a surface for which protection is desired, thereby forming a layer.After formation of the layer, water will readily evaporate or beabsorbed into an adjacent fibrous layer, resulting in a continuous layerof polymer on the surface. This method, however, requires the input of asignificant amount of energy, and further requires the use of relativelyheavy duty equipment.

An improved version of the above-described method incorporates excesswater in the initial mixing step, which results in plasticizedpolymer-in-water. Sufficient water is then slowly evaporated whilemixing and heating, resulting in an inversion to water-in-oilplasticized polymer. Finally, water is added back, with mixing andheating, resulting in a reversion to a final oil plasticizedpolymer-in-water or an abbreviated oil-in-water emulsion (see, forexample, U.S. Pat. No. 2,532,223). This method uses relatively lowamounts of energy.

Other conventionally used methods of producing polymer dispersionsinclude using an alkyl aryl alkali metal sulfonate agent and only asingle inversion (see, for example, U.S. Pat. No. 2,611,755), as well asusing a single inversion in combination with little or no plasticizer(see, for example, U.S. Pat. No. 3,234,161).

Various other methods of mixing and compounding polymeric materials havebeen reported, including methods that use screw extruders to mixpolymeric compounds lacking water (see, for example, WO00/71608, U.S.Pat. No. 6,512,024, and WO00/71609) and screw extruders that mixpolyol-based compounds (see, for example, U.S. Pat. No. 6,613,827 andWO02/28937).

Conventional methods, however, are time-consuming and energy intensive.What are needed in the art are methods and devices for rapid andeconomical production of polymer dispersions.

SUMMARY OF THE INVENTION

The present invention is directed to the use of continuous extrusiondevices to form high quality polymer dispersions. Screw extruder devicesof the present invention inject water into a zone of high pressure,temperature, and shear to cause the rapid inversion of a weld in lessthan, for example, one minute, which compares very favorably withconventional batch methods, which can take, for example, two or morehours to complete an inversion. This rapid inversion—a surprising resultgiven the extended time inversion requires in batch processes—allows forthe continuous production of polymer dispersions.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph showing a particle size distribution for a polymerdispersion.

FIG. 2 is a graph showing a particle size distribution for a polymerdispersion.

FIG. 3 is a graph showing a particle size distribution for a polymerdispersion.

FIG. 4 is a graph showing a particle size distribution for a polymerdispersion.

FIG. 5 is a graph showing a particle size distribution for a polymerdispersion.

FIG. 6 is a graph showing a particle size distribution for a polymerdispersion.

FIG. 7 is a graph showing a particle size distribution for a polymerdispersion.

FIG. 8 is a graph showing a particle size distribution for a polymerdispersion.

DETAILED DESCRIPTION

The present invention is directed to devices and methods thatefficiently produce polymer dispersions in a continuous process. As usedherein, a “polymer emulsion” refers to a polymer that has beenplasticized with an oil, for example castor oil, and then emulsified inwater. As used herein, a “polymer suspension” refers to a polymer, whichhas not been plasticized with an oil, that has been dispersed in water.Polymer dispersions include both polymer emulsions and polymersuspensions.

Devices of the present invention include screw extruders that arecapable of producing the appropriate temperature, pressure, and shearfor optimal mixing of materials, such as single screw and multiple screwextruders. In preferred embodiments, a twin screw extruder is used. Twinscrew extruders are well known in the art and can be readily configuredin a virtually limitless number of permutations to achieve many desiredeffects.

Screw extruders of the present invention are configured, in variousembodiments, to allow for the introduction of several separatecomponents that are mixed in a first zone. In various embodiments,thermoplastic polymer resin, surfactant, and initial water areintroduced into the screw extruder and are mixed in a first zone. Invarious embodiments, plasticizer is also added. In yet furtherembodiments, other agents and components can be added prior to mixing inthe first zone.

As used herein, a “zone” within an extruder is a section of the lengthof the extruder that is configured to perform a discrete function. Inthe case of the first zone just described, the function is to thoroughlymix the resin, surfactant, plasticizer if included, and initial water toform a weld. A zone can have one or more subzones, for example, in whicha portion of the function of the zone is performed. For example, thefirst zone can have two or more subzones in which one or more of thecomponents are added and/or mixed to achieve the desired result.

As used herein, a “weld” is the homogeneous dispersion ofwater-in-polymer or water-in-oil plasticized polymer formed from thethorough mixing of the starting components.

Components can be introduced into the extruder by any suitable,conventional method. For example, solid materials such as polymer resinscan be fed into the extruder through a port provided with aloss-in-weight feeder, and liquids can be gravity fed or injected intothe extruder. It is usually desired to convey polymer in first and thento introduce the plasticizer (if any), surfactant, and some initialwater. These initial ingredients can optionally be introduced, forexample, using gravity feed or under pressure. The plasticizer,surfactant, and initial water may be combined as an emulsion to injectas a single feed.

As will be described in more detail below, water injection pointslocated in the weld inversion zone are preferably configured to injectwater at high pressure, and, specifically, at a pressure higher than thepressure of the zone into which the water is being injected. As usedherein “adding water” includes any conventional method of introducingwater into a screw extruder, and in preferred embodiments, “addingwater” means injecting water at a high pressure greater than that of thezone pressure into which the water is added.

In various embodiments of the present invention, the weld inversion zoneincludes one, two, or more subzones comprising one or more intermediatewater injection points. These intermediate water injection points allowfor the gradual mixing of water into the weld prior to inversion, whichprovides for a more homogeneous sand finer dispersion of water dropletsprior to the inversion point. Pressures and temperatures for theseintermediate water injection subzones can be, for example, the same asfor elsewhere within the weld inversion zone.

In various embodiments, a segmented, co-rotating, closely intermeshedand self-wiping twin screw extruder is used for the process of thepresent invention. In various embodiments, two and three lobe designsare used. A 50 L/D ((screw length)/(nominal screw diameter)) or longerprocess section, for example, can be used for preparation of a weld andsubsequent formation of a polymer dispersion. A screw extruder of anysuitable aspect ratio ((screw outer diameter)/(screw inner diameter))can be used.

In other embodiments, a single screw or counter-rotating extruder isused with the methods of the present invention.

In various embodiments, for example, the first zone can operatepreferably at low temperatures of up to 100° C. and pressures of 2×10⁶Pascal to 4×10⁶ Pascal (300-600 pounds per square inch). The use oftemperatures lower than 100° C. in various embodiments of the presentinvention reduce or eliminate the formation of steam within theextruder, which results in more complete and efficient processing.Higher temperature, of course, can be used in alternative embodiments.

Higher temperatures and pressures can be used with a thermally stablethermoplastic polymer to optimize mixing and weld formation. Also,typically a higher temperature can be used for polymers lacking aplasticizer. Pressure is kept sufficiently high so as to suppress orprevent formation of bubbles of steam. In examples in which aplasticizer is used, comparatively less shearing force is generallyrequired at the same temperature. Shearing rate can be set at, forexample, an average 200 s⁻¹ or higher. The components are generallymoved into and through the first zone in the minimum amount of timerequired to thoroughly mix the components and form the weld, for exampleless than 45, 35, or 30 seconds.

After formation of the weld in the first zone, the weld material ismoved to a second zone. The second zone can be adjacent the first zone,or can be some distance downstream in the extruder. In variousembodiments it is preferred to provide some distance between the firstand second zone, for example with conveying screw elements, which allowsfor the equilibration of weld temperature.

The second zone has means for introducing water to promote fullinversion, which will generally be a port through which the water isinjected at relatively high pressure, for example, at a pressure greaterthan the pressure in the second zone. Injection pressures can be, forexample, 2.67×10⁶ Pascal to 3.33×10⁶ Pascal or 2.67×10⁶ Pascal to 4×10⁶Pascal. The second zone is configured so as to create a hightemperature, high pressure zone in which the weld will undergo aninversion and then be quickly dispersed or emulsified. In variousembodiments, the second zone is maintained at temperatures of, forexample, 70° C. to 90° C., 80° C. to 90° C. or up to 100° C. andpressures of 2×10⁶ Pascal to 4×10⁶ Pascal. Conditions can be chosen, forexample, to allow for the most rapid, complete inversion possible.Components can be within the second zone for any suitable duration, forexample less than 45 seconds, less than 35 seconds, or less than 30seconds. Water injected into the second zone is preferably at atemperature approximating the zone temperature, thereby preventingquenching of the weld.

Further zones can be added downstream in the extruder, as desired, toprovide a convenient method to introduce more water for dilution of thepolymer dispersion, or to introduce agents or other components into thefinal composition.

The product of the screw extrusion process just described is a polymerdispersion that can be used for many purposes, as described elsewhereherein. The devices and processes of the present invention can be usedto produce polymer dispersions having extremely fine particle size,which is generally considered desirable. For example, the methods of thepresent invention can result in polymer dispersions having most particlediameters less than 10 microns, 7.5 microns, or 5 microns, and with mostparticle diameters between 0.25 and 1.5 microns.

Compositions of the present invention include thermoplastic polymercompositions that can conventionally be formed into a weld and thenformed into a dispersion in water or another liquid.

The polymeric component of dispersions of the present invention cancomprise any conventional thermoplastic polymer, and in variousembodiments, the polymer comprises a poly(vinyl acetal), such aspoly(vinyl butyral), or a polyurethane.

Suitable poly(vinyl acetal)s for the practice of the present inventioncan be obtained, for example and without limitation, by reactingpoly(vinyl alcohol) or a partially hydrolyzed polyvinyl ester with analdehyde. Other poly(vinyl acetal)s, such as the reaction products ofhydrolyzed poly(vinyl ester)s with formaldehyde, acetaldehyde,propionaldehyde, and benzaldehyde, also may be used.

Among the poly(vinyl acetal)s, poly(vinyl butyral) is particularlyuseful. The poly(vinyl butyral)s that are used in accordance with theinvention may vary substantially in their composition. Thus, in someembodiments, poly(vinyl butyral)s may be used that have up to 30%hydroxyl groups by weight, calculated as poly(vinyl alcohol), up to 30%ester groups by weight, calculated as polyvinyl ester, and the balancesubstantially butyraldehyde acetal. In various embodiments, poly(vinylbutyral) containing more than 9% hydroxyl groups by weight, but not morethan 25% hydroxyl groups, calculated as poly(vinyl alcohol) can be used.

According to further embodiments of the present invention, thepoly(vinyl butyral) contains 10-20% hydroxyl groups by weight,calculated as poly(vinyl alcohol), less than 5% acetate groups byweight, calculated as poly(vinyl acetate), with the balancesubstantially butyraldehyde acetal.

The polyvinyl esters from which the poly(vinyl butyral)s are made mayhave widely varying degrees of polymerization as evidenced by theviscosities of solutions thereof. For example, poly(vinyl acetate)s thatare used as a starting material in the sequential processes ofhydrolysis and acetalization to manufacture poly(vinyl butyral) may beused. Other polyvinyl esters may vary correspondingly. In variousembodiments, the resultant polymer used in the dispersion manufactureprocess has a weight average molecular weight of at least 40,000 Daltonsto produce films with desirable mechanical properties.

The ester groups in the poly(vinyl butyral)s are usually acetate groups,but the acetate groups may be wholly or partially replaced by otherester groups such as formate, propionate, butyrate, benzoate, and thelike.

Polymeric resins can be incorporated into polymer dispersions in anysuitable amount, with the end product having a percent solidsconcentration of, for example, from 40% to 70% solids or 40% to 60%solids on a weight per weight basis, with “solids” being defined as thetotal weight of polymer, plasticizer, surfactant, and other agents. Theproportion of the individual components within the total solids aregiven in parts per one hundred parts resin (phr).

Various poly(vinyl butyral) resins are commercially available fromSolutia, Incorporated (St. Louis, Mo.), as Butvar®.

Any plasticizer suitable for use with a chosen thermoplastic polymer ofthe present invention can be used. Useful plasticizers include, but arenot limited to, triethylene glycol di-2-ethylhexanoate, butylricinoleate, castor oil, dibutoxy ethyl phthalate, diethyl phthalate,dibutyl sebacate, dibutyl phthalate, triethylene glycol dihexoate,trioctyl phosphate, triethyl glycol ester of coconut oil fatty acids,phenyl ethers of polyethylene oxide rosin derivatives, oil modifiedsebacic alkyd resins, tricresyl phosphate, and the like. Mixes of theseand/or other plasticizers may also be employed.

Plasticizers can be incorporated in any suitable amount, including someembodiments in which no plasticizer is used, and these amounts include,for example, up to 80 phr, up to 50 phr, up to 30 phr, or from 5-80 or10-40 phr plasticizer.

Any suitable surfactant may also be employed, for example, but notlimited to, reaction products of strong bases and soap forming organicacids in general, sodium oleate, salts of such bases as the alkalimetals, for example sodium hydroxide or potassium hydroxide, ammoniumhydroxide or quaternary ammonium bases, for example, triphenyl methylammonium hydroxide, tetraethyl ammonium hydroxide, and the like,triethanolamine, morpholine, and the like, made with such organic acidsas stearic acid, oleic acid, ricinoleic acid, palmitic acid, lauricacid, dodecyl benzene sulfonic acid, abietic acid, and the like, as wellas, generally, alkyl aryl alkali metal sulfonates. A surfactant that isa combination of an acid and a base may be reacted in-situ in the firstzone of the extruder or prior to injection. In various embodiments, asurfactant mixture is produced in-situ from the following combination oforganic acids: 73% oleic acid, 8% linoleic acid, 6% palmitoleic acid, 3%myristoleic acid, 1% linolenic acid, and 9% C14-C17 saturated carboxylicacids.

In various embodiments, the acid portion is an organic acid having analiphatic chain of at least 10 carbon atoms, for example, 10 to 20carbon atoms, as those given above. Other suitable surfactants can beselected from the general class of water-dispersible surfactants whichare compatible with a poly(vinyl acetal) resin and plasticizer, if any,typical examples of which are aryl alkyl sulfonates, tertiary amines,and ethylene oxide fatty acid condensates.

A surfactant can be incorporated in any suitable amount, including, forexample, 0.5 to 30 phr, 0.5 to 20 phr, or 0.5 to 10 phr, depending onthe surfactant (or co-surfactant if any) used and the other componentsof the dispersion.

Water can be incorporated at the beginning of the process and prior tointroduction into the first zone in a relatively small amount that issufficient to form a water in resin or water in oil composition. Invarious embodiments, the amount of initial water for weld formation isbetween 5% and 25% of the solids weight. In the second zone, whereadditional water is introduced to induce inversion to a polymerdispersion, water is introduced in an amount at least sufficient toallow the inversion to occur. Further water can, of course be added atthat point. Finally, any further amount of water, as desired, can beadded prior to final extrusion to dilute the dispersion. Final inversionoccurs at a solids content of, for example, from 65%-95% or from70%-90%. In various embodiments the minimum water for inversion is usedso as to minimize the energy requirement per unit mass of weld andminimum dispersion particle diameters. Dilution of the aqueous phase isfollowed-up in a subsequent zone or outside of the extruder. In variousembodiments, aqueous dispersions have a solids concentration in theranges given above. In various embodiments, a final solids concentrationon the lower end of the range—for example about 40%—is preferred tomaximize shipping economy. Further dilution can generally be performedat the point of application of the polymer dispersion.

Other agents and additives can optionally be included at any suitablestage of processing, including, but not limited to, fillers, modifyingagents, starches, clays, natural gums, synthetic thickeners, and thelike.

Devices and methods of the present invention provide several significantadvantages over conventional batch process methods and devices. Thepresent invention allows for the continuous and relatively extremelyrapid production of a polymer dispersion. Whereas prior art methodscould require two or more hours of high energy mixing to provokeinversion of a weld, the present invention provides devices and methodsthat allow the inversion to occur within a minute, thereby significantlyreducing both production time and energy requirements. A furtheradvantage of the invention, as is evidenced by the examples, is thedesirably small and narrow distribution of particle sizes, which allowsfor the formation of improved films and reduces the amount of filteringrequired to produce an end product.

The present invention includes extruder devices, and particularly twinscrew extruder devices, that are configured as disclosed elsewhereherein to produce a polymer dispersion, which can be a suspension or anemulsion, under the specified conditions.

The present invention includes methods of producing a polymerdispersion, comprising using any of the devices of the present inventionto form a polymer dispersion.

The present invention also includes films and other coatings andapplications of polymer dispersions produced by the methods of thepresent invention and/or devices of the present invention.

Example 1

A Berstorff ZE-25A twin screw extruder with aspect ratio of 1.45 is setup to provide a weld formation zone and a weld inversion zone. The weldformation zone is configured to accept polymer resin, plasticizer,surfactant, and a portion of the final water weight. The weld inversionzone is configured with two water injection ports. The zone temperaturesfor the twin screw extruder are 75° C. to 95° C. The water for injectionpoints is preheated to 65° C. to 75° C.

The following components are added to the extruder and passed throughthe first zone in less than about 10 seconds: 101.3 grams per minuteButvar® B-72 Resin, 51.0 grams per minute castor oil, 20.6 grams perminute Petronate L surfactant (Crompton Corp., Middlebury, Conn.), and20.4 grams per minute initial water. A further 52.9 grams per minute(105.8 total) of water are introduced under pressure at each waterinjection point in the weld inversion zone.

The weld is then further dispersed by hand into about 80% water afterdischarge from the extruder.

The resulting polymer dispersion has the following particlecharacteristics, as measured with a Horiba LA-910 particle sizeanalyzer:

Particle Diameter in Microns for Particle Diameter in Microns forCumulative Length Percent Cumulative Volume Percent 10% 50% 90% 10% 50%90% 0.199 0.316 0.463 0.266 0.405 1.461

These results are shown graphically in FIGS. 1 (cumulative length) and 2(cumulative volume).

Moisture content of the weld product prior to hand dispersing ismeasured with a Mettler Toledo HR 73 Halogen Moisture Analyzer to be27.31 percent.

After dispersing by hand, the polymer dispersion is sieved through aNumber 80 sieve with an opening of 180 microns, and a Mettler Toledo HR73 Halogen Moisture Analyzer is used to measure the solids contents ofrejects and accepts according to the following table:

Wet Weight (weight percent) Solids Content (weight percent) AcceptsRejects Accepts Rejects 98.64 1.36 2.53 Not Measured

Example 2

A Berstorff ZE-25A twin screw extruder is set up to provide a weldformation zone and a weld inversion zone. The weld formation zone isconfigured to accept polymer resin, plasticizer, surfactant, and aportion of the final water weight. The weld inversion zone is configuredwith two water injection ports. The zone temperatures for the twin screwextruder are 75° C. to 95° C. The water for injection points ispreheated to 65° C. to 75° C.

The following components are added to the extruder, passed through thefirst zone in less than about 10 seconds, through the second zone, andthen extruded as a dispersed polymer, which is sampled at two timepoints (A and B):

The following components are added to the extruder and passed throughthe first zone in less than about 10 seconds: 101.3 grams per minuteButvar® B-72 Resin, 51.0 grams per minute castor oil, 20.6 grams perminute Petronate L surfactant (Crompton Corp., Middlebury, Conn.), and20.4 grams per minute initial water. A further 94.5 grams per minute(189.0 total) of water are introduced under pressure at each waterinjection point in the weld inversion zone.

The resulting polymer first sample dispersion at time point A has thefollowing particle characteristics, as measured with a Horiba LA-910particle size analyzer:

Particle Diameter in Microns for Particle Diameter in Microns forCumulative Length Percent Cumulative Volume Percent 10% 50% 90% 10% 50%90% 0.183 0.286 0.422 0.268 1.202 14.723

These results are shown graphically in FIGS. 3 (cumulative length) and 4(cumulative volume).

The polymer dispersion samples from time points A and B (initial andafter more time) are sieved through a Number 80 sieve with an opening of180 microns, and a Mettler Toledo HR 73 Halogen Moisture Analyzer isused to measure the solids contents of rejects and accepts according tothe following table:

Time Wet Weight (weight percent) Solids Content (weight percent) PointAccepts Rejects Accepts Rejects A 87.32 12.68 11.85 Not Measured B 90.989.02 34.44 30.81

A sieved sample of time point B is hand poured into a steel dish, whichis placed in a level position. After evaporation of the water, the castfilm formed is examined and determined to be of a quality approximatingthat of films formed from commercially available dispersions.

Example 3 Comparative

Commercially available poly(vinyl butyral) dispersion RS-261 fromSolutia, Incorporated is analyzed and is determined to have thefollowing particle characteristics, as measured with a Horiba LA-910particle size analyzer:

Particle Diameter in Microns for Particle Diameter in Microns forCumulative Length Percent Cumulative Volume Percent 10% 50% 90% 10% 50%90% 0.186 0.317 0.553 0.314 1.314 5.486

These results are shown graphically in FIGS. 5 (cumulative length) and 6(cumulative volume).

Example 4

A Berstorff ZE-40A twin screw extruder with aspect ratio of 1.46, whichis a larger extruder than the ZE-25A used in Examples 1 and 2, is set upto provide a weld formation zone and a weld inversion zone. The weldformation zone is configured to accept polymer resin, plasticizer,surfactant, and a portion of the final water weight. The weld inversionzone is configured with two water injection ports. A third waterinjection port is located after the weld inversion zone for furtherdilution of the dispersion. The zone temperatures for the twin screwextruder are 70° C. to 80° C. The water for injection points ispreheated to 65° C. to 75° C.

The following components are added to the extruder and passed throughthe first zone in less than about 10 seconds: 408.2 grams per minuteButvar® B-72 Resin, 205.6 grams/minute castor oil, 83.2 grams per minutePetronate L surfactant (Crompton Corp., Middlebury, Conn.), and 81.6grams per minute initial water. 75.6 grams per minute are added at thefirst water injection point, 113.4 grams per minute are added at thesecond water injection point, and 483.8 grams per minute are added atthe third water injection point (for dilution after the weld inversionzone).

The resulting polymer dispersion has the following particlecharacteristics, as measured with a Horiba LA-910 particle sizeanalyzer:

Particle Diameter in Microns for Particle Diameter in Microns forCumulative Length Percent Cumulative Volume Percent 10% 50% 90% 10% 50%90% 0.218 0.361 0.570 0.321 0.592 3.173

These results are shown graphically in FIGS. 7 (cumulative length) and 8(cumulative volume).

The polymer dispersion is sieved through a Number 80 sieve with anopening of 180 microns, and a Mettler Toledo HR 73 Halogen MoistureAnalyzer is used to measure the solids contents of rejects and acceptsaccording to the following table:

Wet Weight (weight percent) Solids Content (weight percent) AcceptsRejects Accepts Rejects 98.93 1.07 41.84 Not Measured

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiments disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

It will further be understood that any of the ranges, values, orcharacteristics given for any single component of the present inventioncan be used interchangeably with any ranges, values, or characteristicsgiven for any of the other components of the invention, wherecompatible, to form an embodiment having defined values for each of thecomponents, as given herein throughout. For example, a polymer resin canbe formed comprising residual hydroxyl content in any of the rangesgiven in addition to any of the ranges given for plasticizer, whereappropriate, to form many permutations that are within the scope of thepresent invention but that would be cumbersome to list.

Any figure reference numbers given within the abstract or any claims arefor illustrative purposes only and should not be construed to limit theclaimed invention to any one particular embodiment shown in any figure.

Figures are not drawn to scale unless otherwise indicated.

Each reference, including journal articles, patents, applications, andbooks, referred to herein is hereby incorporated by reference in itsentirety.

We claim:
 1. A method for producing a dispersion of poly(vinyl butyral)in water comprising: (a) feeding said poly(vinyl butyral), aplasticizer, a surfactant, and initial water into a screw extruder; (b)mixing said poly(vinyl butyral), said plasticizer, said surfactant, andsaid initial water in a first zone within said screw extruder to form aweld, wherein said weld forms in less than 45 seconds; and (c)contacting additional water with said weld in a second zone within saidscrew extruder to thereby cause an inversion of said weld and theformation of said dispersion.
 2. The method of claim 1, wherein saiddispersion comprises particles, wherein most of said particles have adiameter of less than 5 microns.
 3. The method of claim 1, wherein saiddispersion comprises particles, wherein most of said particles have adiameter in the range of 0.25 to 1.5 microns.
 4. The method of claim 1,wherein said first zone is set at a pressure of 2×10⁶ Pascal to 4×10⁶Pascal and a temperature below 100° C.
 5. The method of claim 1, whereinsaid second zone is set at a pressure of 2×10⁶ Pascal to 4×10⁶ Pascaland a temperature below 100° C.
 6. The method of claim 1, wherein saidsecond zone is maintained at a temperature of 70° C. to 90° C.
 7. Themethod of claim 1, wherein said weld forms during said mixing of step(b) in less than about 35 seconds.
 8. The method of claim 1, whereinsaid dispersion forms in less than about 45 seconds during saidcontacting of step (c).
 9. The method of claim 1, wherein saiddispersion forms in less than about 35 seconds during said contacting ofstep (c).
 10. The method of claim 1, wherein said dispersion comprisesan emulsion of said poly(vinyl butyral).
 11. The method of claim 1,wherein said contacting of step (c) comprises mixing said weld with saidadditional water.
 12. The method of claim 1, wherein said screw extruderis a twin screw extruder.
 13. A method for producing a dispersion of athermoplastic polymer in water comprising: (a) feeding saidthermoplastic polymer, a surfactant, a plasticizer, and initial waterinto a screw extruder, wherein said thermoplastic polymer comprises apoly(vinyl acetal) or polyurethane; (b) mixing said thermoplasticpolymer, said surfactant, said plasticizer, and said initial water in afirst zone within said screw extruder to form a weld, wherein said weldforms in less than 45 seconds; and (c) contacting additional water withsaid weld in a second zone within said screw extruder to thereby causean inversion of said weld and the formation of said dispersion, whereinsaid first zone is set at a pressure of 2×10⁶ Pascal to 4×10⁶ Pascal,wherein said second zone is set at a pressure of 2×10⁶ Pascal to 4×10⁶Pascal.
 14. The method of claim 13, wherein said dispersion comprisesparticles, wherein most of said particles have a diameter of less than10 microns.
 15. The method of claim 13, wherein said dispersioncomprises particles, wherein most of said particles have a diameter inthe range of 0.25 to 1.5 microns.
 16. The method of claim 13, whereinsaid weld forms during said mixing of step (b) in less than about 35seconds.
 17. The method of claim 13, wherein said dispersion forms inless than about 45 seconds during said contacting of step (c).
 18. Themethod of claim 13, wherein said dispersion forms in less than about 35seconds during said contacting of step (c).
 19. The method of claim 13,wherein said thermoplastic polymer comprises poly(vinyl butyral). 20.The method of claim 13, wherein the temperature of said first zone andsaid second zone is below 100° C.
 21. The method of claim 13, whereinsaid screw extruder is a twin screw extruder.